Field of the Invention
The invention relates to a method for producing a product having an uneven microstructure on a surface thereof, a mold release treatment method, and an active energy ray curable resin composition for mold surface release treatment.
Description of Related Art
In recent years, it is known that the products with the uneven microstructure thereon present antireflection effects, lotus effects and the like, whereas the period of the uneven microstructure is equal to or less than the wavelength of visible light. Particularly, because the refractive indices keep increasing continuously from the refractive index of the air to the refractive index of the product, the uneven structure that is constructed with approximately convex cone structures, so-called the moth-eye-structure, becomes an effective antireflection means.
As a method of forming an uneven microstructure on the surface of the product, the following method arouses interest: a mold having an uneven microstructure formed on the surface thereof (also called a metallic mold, and will be called “mold” in this disclosure hereinafter) is used and the uneven microstructure of the mold is transferred to the surface of the product. In details, a liquid active energy ray curable resin composition is inserted between the substrate and the mold having the uneven microstructure on the surface thereof, the active energy ray curable resin composition is cured by irradiation with an active energy ray to form a cured resin layer, onto which the uneven microstructure is transferred, on the surface of the substrate. In aforesaid method, the quality of the releasability of the mold from the surface of the product has a significant impact on the productivity of the product. That is, in the method, when the mold is released from the surface of the cured resin layer, defects may be generated in the transferred uneven microstructure as resin residue occurs on the surface of the mold.
As a method for improving the releasability between the cured resin layer and the mold, the following methods have been proposed.
(1) The method uses the release agent (external release agent) to treat the mold surface at the side formed with the uneven microstructure (Patent Documents 1 and 2).
(2) The method adds a release agent (internal release agent) to the material constituting the product.
However, for the method of (1), the following problems exist.
(i) After applying a dilute solution of the release agent to the mold or immersing the mold in a dilute solution of the release agent, it is necessary to dry up the mold, which makes the release treatment become time consuming and complicated.
(ii) Uneven treatment such as uneven drying of the release agent may be caused.
(iii) The release agent on the surface of the mold is likely to transit to the surface of the product.
(iv) As the release agent is not sufficiently spread out to every corner of the uneven microstructure of the mold, it is difficult to treat uniformly and sufficiently the region of the uneven microstructure of the mold with the release agent. In addition, when an extraneous substance is attached to the region of the uneven microstructure of the mold, it is difficult to use the release agent to treat the portion adhered with the extraneous substance. Therefore, for the portion of the mold surface being insufficiently treated with the release agent, defects may occur in the transferred uneven microstructure. In addition, for the portion of the mold surface being insufficiently treated with the release agent, the cured resin may be cracked and have residue, resulting in the occurrence of defects in the uneven microstructure itself of the mold. Hence, under the circumstance of using the same mold continuously, defects may be repeated over and over.
Furthermore, for the method (2), the following problems exist.
(v) Because the addition amount of the release agent is set to make the contamination degree of the release agent on the surface of the product not an issue, the releasability may be insufficient.
(vi) On the other hand, when the release agent is added in excess, the surface of the product is contaminated by the release agent and the product is generated with a poor appearance.
As a method of removing extraneous substances attached to the region of the uneven microstructure of the mold, the following method has been proposed.
(3) An adhesion member that has higher adhesion to the mold than to the substrate is pressed against the mold surface at the side formed with the uneven microstructure (Patent Document 3).
However, in the method (3), because the adhesion member that has higher adhesion to the mold than to the substrate is used, there is a possibility that the adhesion member adheres to the mold (i.e. the resin residue occurs). Further, in order to prevent the adhesion member from adhering to the mold (the resin residue), the surface of the mold is treated with the release agent (external release agent) in advance; however, the problem that it is difficult to treat the portion attached with extraneous substances with the release agent still remains. In addition, the release agent is peeled off from the mold by the adhesion member, along with the extraneous substances. In this way, in the method (3), even if the extraneous substances may be removed, defects may occur in the transferred uneven microstructure due to the peeling of the release agent from the mold or the adhesion of the adhesion member to the mold.